1. Field of the Invention
The present invention relates generally to bipolar transistors and more specifically to a vertical inverted bipolar transistor being radiation hardened and having high emitter to base breakdown voltage.
2. Description of the Prior Art
Lateral bipolar transistors generally have a high emitter to base breakdown voltage and a high current gain or beta but lateral transistors are not radiation hardened. Radiation hardened elements are those which have a current gain greater than ten and slowly degrades with neutron radiation, minimizes transient gamma photocurrents and have a surface insensitive to ionizing radiation. Lateral transistors are generally very sensitive to radiation because of the wide base width and other surface related effects.
Generally, vertical transistors have high current gains or beta and are very radiation hardened, but they have a relatively low emitter to base breakdown voltage. Radiation hardness is the result of the very narrow active base width. The major use of inverted vertical transistors has been in integrated injection logic and is generally included in a complementary pair of bipolar transistors.
Though lateral transistors have a high emitter to base breakdown voltage and high current gains, they are not radiation hardened and while vertical transistors are radiation hardened and have high current gain, they do not have a high emitter to base breakdown voltage. Thus there exists a need for a bipolar transistor structure which has a high emitter to base breakdown voltage, a high current gain, and which is radiation hardened.